A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In lithographic systems, a substrate track may be connected directly to the lithographic apparatus. Such a substrate track comprises one or more processing devices, which are configured to (automatically) process substrates. A substrate handler, for instance a substrate robot or an interface unit may be provided to transfer substrates between the substrate track and the lithographic apparatus to introduce a substrate from the substrate track into the lithographic apparatus, and to transfer a substrate, which has been exposed, from the lithographic apparatus to the substrate track.
In a lithographic system, the flow of substrates through the substrate track and the lithographic apparatus is typically designed in such a way that a substrate enters the substrate track at a particular input location, after which the substrate passes one or more processing devices before being transferred to the lithographic apparatus for exposure. Thereafter, the substrate is transferred back to the substrate track where it is taken out of the substrate track after the substrate has passed one or more processing devices. During optimal production there is a continuous flow of substrates through the lithographic system.